CVE-2021-47865Public exploitNetwork attack vectorHinoki check available

Service interruption via connection allowance exhaustion

Published Jan 21, 2026 · Updated Jan 21, 2026

Denial of service in ProFTPD 1.3.7a allows remote attackers to block legitimate FTP access by exhausting available connections. The published script continuously starts threaded FTP clients, consuming the server's finite connection allowance until new sessions are refused. No authentication is required; exposure depends on a reachable FTP listener and ineffective connection limits, and the bounded result is service interruption rather than data access.

CVSS severity8.7
High
EPSS probability0.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Denial of service in ProFTPD 1.3.7a allows remote attackers to block legitimate FTP access by exhausting available connections. The published script continuously starts threaded FTP clients, consuming the server's finite connection allowance until new sessions are refused. No authentication is required; exposure depends on a reachable FTP listener and ineffective connection limits, and the bounded result is service interruption rather than data access.

The record

CVE
CVE-2021-47865
Published
Jan 21, 2026
Updated
Jan 21, 2026
Vendor
ProFTPD Project
Product
ProFTPD
Classifications
CWE-770, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 21, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.3.7a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ProFTPD Project · ProFTPDversion=1.3.7a

Published CVSS scores

7.5VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.003Application Exhaustion Flood

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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